Drive circuit for counter tubes



Nov. 27, 1962 R. J. PAsco 3,066,240

DRIVE CIRCUIT FOR COUNTER TUBES Filed March 10, 1960 INVENTOR ,LsEc ,Lssc RICHARD J. PASCQ ATTORNEY United States Patent Ofilice 3,055,240 Patented Nov. 27,1962

3,666,240 DRIVE ClRCUIT FOP. COUNTER TUBES Richard J. Pasco, South Williamsport, Pa., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Mar. 10, 1960, Ser. No. 14,025 5 Claims. (Cl. 315-846) This invention relates to electronic counting devices and more specifically to a pulse forming network suitable for driving gas-filled glow transfer counting tubes.

A convenient device for counting electrical impulses is the multi-stable glow discharge transfer tube which incorporates several counting stages within one tube envelope. These tubes are generally, although not necessarily, constructed to provide for a count of ten and may be cascaded to provide a decimal counting system to any order of magnitude desired. By way of example, a decade counting tube of this type, such as 6476 manufactured by Sylvania Electric Products Inc., comprises a central anode and three sets or groups of cathodic electrodes arranged in a circle about the anode. One set of the cathodic electrodes serves as the main or count indicating cathodes, which may be electrically connected together, but generally one or more are arranged to provide independent electrical outputs. The remaining electrodes (there are normally 30 electrodes in a decade tube) are divided into two groups, the electrodes of each group being connected together to form two sets of guide or trans fer electrodes, with one guide electrode from each group positioned between each pair of adjacent main cathodes. To transfer the glow from one cathode to another, the potential of one set of guide electrodes is lowered to the point where the glow will leave its position on a main cathode and transfer to the nearest guide electrode of that set. The potential of the second set of guide electrodes is then lowered While the potential of the first set is allowed to return to its normal value. When the potential on the second set is sutficiently lower than that on the first set, the glow will transfer from its position on the first guide electrode to the adjacent guide electrode of the second set. The potential of the second set of guide electrodes is then allowed to return to its normal value. The normal potentials on the second set of guide electrodes and on the main cathodes are such that the glow will then move from the second electrode to the adjacent main cathode, whereby the glow is moved in a predetermined direction from one main cathode via two guide electrodes to the next main cathode to effect a count.

This result is achieved by a so-called driving circuit for the tube, many of which have heretofore been available. The prior art circuits of which the applicant is aware, however, have certain drawbacks and limitations which limit their usefulness and versatility for the variety of counting applications to which the glow transfer counter may be subjected. For example, in one circuit with which applicant is familiar, the pulses applied to the drive circuit must have a duration at least as great as the pulses applied to the guide electrodes; i.e., unless special shaping circuits are provided between the source of pulses to be counted and the drive circuit, the drive circuit is ineffective to generate the necessary transfer pulses for actuation of the counter tube. Also, available drive circuits are sensitive to the rate of occurrence of input pulses with the result that there is a variation in displacement of the essentially overlapping pulses applied to the guide electrodes as the repetition rate of the pulses to be counted varies. Finally, prior art drive circuits require the application of input pulses of undesirably large amplitude, making it necessary in some applications to amplify the pulses to be counted prior to their application to the drive circuit.

It is an object of this invention to provide a more reliable and elficient network for suitably energizing the guides of the glow transfer counting tube than has heretofore been available.

Another object of this invention is to provide a network for forming two distinct voltage pulses in response to a single input voltage pulse which have the same pulse amplitude, duration, and phase relationship regardless of the randomness of the input pulses, within the counting limitations of the counter tube involved.

Another object of the invention is to provide a pulse forming network for forming two voltage pulses of sub stantially the same duration and amplitude, the leading edge of the second pulse coinciding with the trailing edge of the first pulse, in response to a single input pulse of smaller amplitude and duration than are required to trigger available counter tube drive circuits.

Other objects, features and advantages of the invention, and a better understanding of its operation, will be apparent from the following description considered in connection with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of the pulse forming network of this invention, in combination with a glow transfer counter tube; and

FIG. 2 is a diagram illustrating the shape of the pulses generated by the network of FIG. 1. r

The gas filled glow transfer counting tube 163 shown in the drawing includes a disc shaped anode 12 surrounded by slim rod-like cathodic elements arranged in'a circle about the anode. In a decade counter having thirty elements, each third electrode is designated as a main or count-indicating cathode, and are shown in the drawing at 14, 16, 18 32. The remaining cathodic electrodes are divided into two groups, all of the members of each group being connected together to form two sets of guide or transfer electrodes, these electrodes in the interest of clarity, being schematically illustrated as only two electrodes 34 and 36. One guide electrode in each of the groups is mounted adjacent each main cathode. In other Words, between successive main cathodes, between 14 and 16 for example, are positioned two guide elec trodes, one associated with group 34 and the other asso* ciated with group 36.

The anode 12 is connected through a resistor 38 to a source of positive potential indicated by terminal 40, which may have a value of about +410 volts. Cathodes 14, 16 30 are connected to ground through resistor 33 for developing an output pulse for each ten input pulses applied to the circuit. The potential between the anode 12 and the cathodes is sufficient to establish a glow discharge between the anode and the cathode at which the highest voltage gradient exists. It is the function of the guide electrodes 34 and 36 and the pulse forming circuit coupled thereto to transfer the glow from the cathode at which it is invested to successive adjacent cathodes in response to input pulses to be counted.

The pulse forming network according to the invention includes a triple triode electron tube, such as a 6EZ8, each of the sections 42, 44 and 46 of which. has an anode, a cathode and a control grid. The anodes: of triode sections 42, 44 and 46 are respectively connected through resistors 48, 50 and 52 to a source of positive potential, represented by terminal 54, of a magnitude, by way of example, of +45 volts. The cathodes of the three triode sections have a common cathode resistor 56 connected to a source of negative potential, represented by terminal 58, having a value, in the described embodiment, of 225 volts. The anode of triode section 42 is coupled to the control grid of triode section 44 by capacitor. 60,

the grid also being coupled to the voltage supply 54 through resistor 62. The anodes of triode sections 42 and 46 are respectively connected to guide electrodes 34 and 36 of counter tube 10, and the anode of triode section 42 is also coupled via capacitor 64 and resistor 66 to the control grid of triode section 46. The control grid of triode 42 is connected through resistor 68 and resistor 70 to potential source 54, and through resistor 68 and 72 to potential source 58. The junction of capacitor 64 and resistor 66 is also connected to potential source 58 through resistor 74.

In operation, the present drive circuit, in response to a single input pulse, generates a pair of negative voltage pulses of substantially equal amplitude and duration to lower in sequence the potential of a pair of adjacent guides 34 and 36 of counter tube 10. The pulses to be counted, indicated at 80, which may be positive pulses of an amplitude as little as 7 volts and a duration as short as 2 microseconds, are applied through capacitor 82 and resistor 68 to the control grid of triode section 42. Triode sections 42 and 44 are connected as a oneshot multivibraor, vw'th section 42 biased off and section 44 conducting heavily in the quiescent condition. In

this embodiment, approximately 7 volts bias is provided for triode section 42 whereby an input pulse 80 having an amplitude of at least 7 volts initiates the regenerative action which drives the anode current of this triode to saturation. This anode being connected to guide 34, the potential of guide 34 will be decreased for the duration of the negative pulse 84, which is, in effect, applied between guide 34 and ground. As a result, the glow is attracted to guide 34, and moves away from the cathode at which it was invested.

The negative pulse 84 is also coupled via capacitor 60 to the control grid of triode section 44, and is of sufficient amplitude to turn section 44 off. When section 44 is cut off, cathode coupling to triode section 42 causes the latter to be turned off, the period of pulse 84 being determined by the parameters of the one-shot multivibrator circuit. As shown in FIG. 2, the pulse 84 is of substantially rectangular waveform having a fast rise time from a level of approximately +45 volts to a level of about 100 volts and a duration of about 80 microseconds. Because of the regenerative nature of the oneshot multivibrator, the waveform of pulse 84 is essentially independent of the wave shape of input pulse 80 so long as the latter is of suflicient amplitude to trigger triode section 42 on, and shorter than the desired duration of pulse 84.

A portion of the pulse 84 is also coupled over condoctor 86 and through a differentiating circuit including capacitor 64 and resistor 74 to the control grid of triode section 46. Since triode section 46 is biased to cut-01f by the constant currents in common cathode resistor 56 during the generation of pulse 84, the negative portion of waveform 88 may be neglected. When, however, the pulse on the grid of triode section 46 goes positive, the triode section is driven into saturation. The negative portion of waveform 88 being of the same duration as pulse 84, the positive going pulse of waveform 88 is coincident with the trailing edge of pulse 84. Conduction of triode section 46 produces a negative pulse 90 at its anode, which is applied between guide electrode 36 and ground to draw the glow from guide 34 and nearer the next adjacent cathode. With the cessation of pulse 90, the glow will completely transfer to the next adjacent cathode. Since the amplitude of pulse 84 is always substantially constant regardless of the input rate, the values of capacitor 64 and resistor 74 can be selected to make pulse 90 identical with pulse 84. Returning the anodes of the three triode sections to a potential of +45 volts afiords the required bias for proper operation of counter tube 10.

In a circuit which has been satisfactorily operated with a Sylvania 6476 counter tube over a range of input pulse frequency from zero to 5000 pulses per second, the values of the circuit components were as follows:

From the foregoing it is seen that the described pulse forming circuit responds to low amplitude input pulses of short duration, of a shape known as a trigger pulse or spike, to produce two voltage pulses of ideal duration and amplitude for reliable counter tube operation. So long as the input pulses are not of such large amplitude as to overdrive the first triode section, or of a duration longer than the desired output pulses, the circuit is essentially insensitive to the pulse shape and amplitude of the input pulses. That is, the circuit will accept input pulses varying in amplitude over a considerable range and varying in duration from a spike to a pulse almost 80 microseconds long (in the disclosed embodiment) and produce idea1" glow transferring pulses over the operating frequency range of the counter tube itself, regardless of the randomness of the input pulse train. If it is necessary to count input pulses having a duration longer than the desired glow transferring pulses, the size of coupling capacitor 82 may be selected to differentiate the input pulse across the grid resistor 72 to obtain a short trigger for initiating the regenerative action of the circuit.

Although a triple triode electron discharge device such as the 6EZ8 and the described associated circuitry is preferred because of its compactness, separate triodes, or transistors, may also be used in the circuit. A pentode-triode type tube might also be used, with appropriate circuit modification, using the pentode section as a Van der Pol oscillator and the triode as a saturation amplifier, produce the successive pulses.

Also, although multivibrators are normally triggered in the grid circuit as illustrated, the present circuit is not intended to be thus limited. Short negative pulses might also be applied to the anode of triode 42 or to the grid of triode 44 to trigger the circuit, in accordance with known mutivibrator techniques, without departing from the spirit of the invention.

What is claimed is:

1. A system for counting electrical pulses comprising, in combination, a glow discharge counting tube having a plurality of cathodes and a pair of guide electrodes for each of said cathodes, corresponding ones of which are connected together, and a pulse forming circuit operative in response to input electrical pulses for driving said counting tube comprising a one-shot multi-vibrator circuit operative in response to an input pulse applied thereto to generate a first negative voltage pulse of uniform amplitude and duration substantially independent of the waveform of said input pulse, means for applying said first negative pulse to one of the guide electrodes in each of said pairs to lower its potential for the duration of said first pulse, a triode electron discharge device having at least an anode circuit and a control circuit, means including a differentiating circuit for impressing said first negative voltage pulse on said control circuit to initiate an increase in the flow of current in said triode in coincidence with the trailing edge of said first negative pulse and produce a second negative voltage pulse having substantially the same amplitude and duration as said first pulse, and means for applying said second negative voltage pulse to the other guide electrode in each of said pairs.

2. A system for counting electrical pulses comprising, in combination, a glow transfer counting tube having a plurality of cathodes and a pair of guide electrodes for each of said cathodes, corresponding ones of which are connected together, and a drive circuit for said counting tube comprising first, second and third electron discharge devices having a common cathode circuit and each having an anode circuit and a control circuit, means interconnecting said first and second discharge devices as a one-shot multivibrator, means for applying positive input pulses to be counted to the control circuit of said first discharge device, said multivibrator being operative in response to an input pulse to produce at the anode of said first discharge device a first negative voltage pulse of uniform amplitude and duration substantially independent of the waveform of said input pulses, means for applying said first negative pulse to one of the guide electrodes in each of said pairs to lower its potential for the duration of said first pulse, means including a differentiating circuit for impressing said first pulse on the control circuit of said third discharge device to initiate an increase in the flow of current in the anode circuit thereof in coincidence with the trailing edge of said first negative pulse and produce a second negative voltage pulse having substantially the same amplitude and duration as said first pulse, and means for applying said second negative voltage pulse to the other guide electrode in each said pairs.

3. A system for counting electrical pulses, comprising, in combination, a glow discharge counter having an anode, a plurality of cathodes, and a pair of guide elec trodes for each of said cathodes, corresponding ones of said guide electrodes being connected together, a source of voltage connected to said anode to produce a glow discharge between said anode and one of said cathodes, and a pulse forming network for alternately decreasing the potential of the guide electrodes in each of said pairs in succession in response to each electrical pulse to be counted to successively transfer the glow from one of said cathodes to another, said pulse-forming circuit including a regenerative circuit operative in response to the application thereto of a pulse to be counted to generate a first negative voltage pulse having amplitude and duration substantially independent ofthe waveform of the pulse to be counted, means for applying said first negative pulse to one of the guide electrodes in each of said pairs to lower its potential for the duration of said first pulse, a triode electron discharge device having an anode circuit and a control circuit, means biasing said triode to be normally non-conducting, means including a difierentiating circuit for impressing said first negative pulse on the control circuit of said triode to increase the current flow in the anode circuit of said triode in coincidence with the trailing edge of said first negative voltage pulse and produce a second negative voltage pulse having substantially the same amplitude and duration as said first negative pulse, and means for applying said second negative pulse to the other guide electrode in each of said pairs to lower its potential subsequent to the firstmentioned ones of said guides.

4. A system for counting electrical pulses comprising, in combination, a glow discharge counter having an anode, a plurality of cathodes and a pair of guide. electrodes for each of said cathodes, means interconnecting corresponding ones of said guide electrodes, a source of voltage connected to said anode to produce a glow discharge between said anode and one of said cathodes, and a pulse forming network for alternately successively decreasing the potential of the guide electrodes in each of said pairs in response to each of said electrical pulses for successively transferring the glow from one of said cathodes to another, said pulse forming network including first, second and third triode electron discharge devices each having an anode, a cathode, and a control grid, a common cathode resistor connected to the cathodes of said three triodes, means interconnecting said first and second triodes as a one-shot multivibrator circuit with said first triode normally non-conducting, means for applying to said first triode electrical pulses of sufiicient amplitude to render said first triode conducting and produce at the anode thereof a first negative pulse of predetermined amplitude and duration, means for applying said first negative pulse to one of the guides in each of said pairs to lower its potential for the duration of said first pulse, means including a differentiating circuit. coupling the anode of said first triode to the control grid of said third triode for applying said first negative pulse to the control grid of said third triode to increase the current flow therein and to produce a second negative voltage pulse at the anode of said third triode having substantially the same amplitude and duration as said first negative pulse, and means for applying said second negative pulse to the other of the guides in each of said pairs to lower its potentials after the first-mentioned ones of said guides.

5. A system for counting electrical pulses of variable rate and wave shape comprising, in combination, a glow discharge counting tube having a plurality of cathodes and a pair of guide electrodes for each of said cathodes, corresponding ones of which are connected together, and a pulse forming circuit for driving said counting tube including a regenerative circuit operative in response to an input pulse which exceeds a predetermined amplitude applied thereto to generate a first negative pulse of substantially fixed amplitude and duration independent of the waveform of the input pulse, means coupling said first negative voltage pulse to one of the guide electrodes in each of said pairs to lower its potential for the dura' tion of said first negative pulse, a normally non-conducting electron discharge device having an anode circuit and a control circuit, means including a difierentiating circuit for coupling said first negative voltage pulse to said control circuit to initiate an increase in the flow of current in said anode circuit in coincidence with the trailing edge of said first negative voltage pulse to produce in said anode circuit a second negative voltage pulse having substantially the same amplitude and duration as said first negative voltage pulse, and means coupling said second negative voltage pulse to the other guide electrode in each of said pairs.

References Cited in the file of this patent UNITED STATES PATENTS 

